Fabrication, characterization, and properties of bionanohybrids based on biocompatible polylactide and carbon nanotubes
This work reports on the preparation and characterization of biodegradable polylactide (PLA) nanocomposites based on functionalized carbon nanotubes (f-MWCNTs). The nanocomposites were prepared by melt extrusion and solvent casting methods. A new method used for the functionalization of multiwalled carbon nanotubes (MWCNTs) with hexadecylamine (HDA) is also reported. Attenuated total reflectance Fourier-transform infrared (ATR-FTIR), Raman, and X-ray photoelectron spectroscopy confirmed the functionalization of the carbon nanotubes. The morphology and structure of the nanocomposites were investigated through scanning electron microscopy (SEM), transmission electron microscopy (TEM), polarized optical microscopy (POM), small angle X-ray scattering (SAXS), and atomic force microscopy (AFM). The influence of functionalized carbon nanotubes on the thermal, thermomechanical and tensile properties of the PLA matrix was also investigated. Firstly, a PLA composite containing 1.5 wt.% of f-MWCNTs (with 10 % amine content, determined gravimatrically) was prepared through a melt extrusion technique. FTIR and Raman spectroscopy revealed the strong interaction between the f-MWCNT’s surfaces and the PLA matrix. The POM (in the molten state) revealed a fairly homogeneous dispersion of f-MWCNTs with some micron-scale agglomeration. POM also revealed that the f-MWCNTs acted as nucleating agents for the crystallization of the PLA matrix. An increase in crystallinity was also observed from differential scanning calorimetry (DSC). Dynamic mechanical analyses (DMA) showed an enhancement of the elastic modulus, particularly above room temperature. An improvement in the tensile strength and elongation at break, without significant loss of modulus, was also reported. Secondly, a composite containing 0.5 wt. % of f-MWCNTs (with 20 % amine content) was prepared by a melt extrusion technique. Improvement of the thermal stability in air was observed. The spherulitic morphology and structure was studied through POM and SAXS. An improvement in the thermomechanical properties was observed below and above the glass transition temperature. The presence of f-MWCNTs played a nucleation role for the crystallization of the polymer matrix. The dispersion was fairly homogeneous in the PLA matrix with some micro-scale agglomeration as observed in SEM. Lastly, a PLA composite with f-MWCNTs (with 10 % amine content) was prepared by a solvent casting method using chloroform as a solvent. The effect of the incorporation of f- MWCNTs on the crystallization behaviour of biodegradable/biocompatible polylactide (PLA) was studied. The crystallization behaviour of the PLA in the absence and presence of f- MWCNTs was studied by using POM, DSC and AFM. The results showed that the f- MWCNTs did not actively nucleate the crystallization of PLA, and that the PLA crystals were perfectly grown in the case of the composite. Such an observation is quite uncommon to the general understanding of the role of CNTs in semicrystalline polymer crystallization.